- Add vars parameter to expandStep for {varname} substitution
- Add mergeVars to combine formula defaults with rule overrides
- Update ApplyExpansions to merge and pass vars for expand/map rules
- Apply var substitution to step ID, title, description, assignee,
labels, and dependencies
- Add comprehensive tests for var overrides functionality
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>